Melanism in cats is caused primarily by two genes: MCIR (see Guest Box 12) and A

Question

Melanism in cats is caused primarily by two genes: MCIR (see Guest Box 12) and ASIP (Agouti Signaling Protein). As we have seen, the dark form is usually dominant if melanism is caused by allelic variation at the MCIR locus. However, melanism is generally recessive if caused by allelic variation at the ACIP locus (Schneider et al. 2012). The melanistic leopard is quite common in some populations of leopards in southeast Asia. The table below shows the inheritance of melanism in the leopard (Panthera pardus) from zoos around the world (Robinson 1970). (a) Based on these data, which gene is responsible for melanism in leopards? Why? (b) Let's assume that that melanism provides cryptic coloration and is selectively advantageous in a particular cat species. Further assume that all individuals are light colored and that mutation rates are equal at these two loci. Which gene is most likely to respond to natural selection for melanism in this population: MCIR or ASIP? Why?

Explanation / Answer

12.7) Melanism caused by two genes: MC1R and ASIP. Melanism is dominant if caused by allelic variation at MC1R locus and it is recessive when it occurs due to allelic variation at ASIP locus.

a) From the data given in the question, the gene responsible for melanism in leopards must be due to dominant variation of MC1R allele. This is because if it is caused by recessive allele, the offsprings in the cross between spotted and black parents will all be spotted. But there are both spotted and black offsprings. The same explanation aplies to the other two crosses.

b) If natural selection occurs, the dominant allele in MC1R locus is most likely to respond because melanism can be expressed even with one allele whereas in case of recessive ASIP, the melanism expression requires the presence of both the alleles.

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